my favorites:
Breathless  //Really great FPS. Made me buy a faster processor for my A1200.
Worms - Director's Cut  //Best Worms game on any platform!
Extreme Racing  //Mode 7 racing game. Like Mario Kart... but better!
Ugh  //Stone Age Taxi sevice! Gravity Force-like.
Universe  //Sci-fi (point&click) adventure game. Really good graphics.
Superfrog  //Great platformer! Super fast!
Alien Breed 3D 2  // Another good FPS. Slow 3D engine tho...
Stunt Car Racer  //Race on tracks high up in the sky! 3D.
Stardust  //Asteroids on steroids! Really good gfx and music. The "warp" sequences are awesome!
Skidmarks  //Good looking and really fun racing game. Top view.
Populous 2  //Strategy game. One of the best. You're GOD!
Settlers  //Another strategy game. 
Lemmings  //Guide your stupid lemmings to the level exit before they jump off a cliff... or get crushed...
James Pond 2  //Good platformer. I played this game a lot!
Indy Heat  //Tiny Race Cars! Pit Crew sounds really funny when you run them over! Up to 4 players.
Heimdall  //Crazy Viking action/adventure!
Gravity Force  //A classic. You really should know about this one. I think there's even a remake for the GP32. Gravity Force 2 (pd/shareware) has 2-player battle mode!
Gobliiins  //Really funny series of adventure games! (point&click)
Frontier - Elite 2  //Best space sim/rpg ever... Until Elite 4 arrives (
frontier.co.uk)
Flashback  //Another World 2. Really good looking and well playing game.
Dragonstone  //Action/adventure. Japanese rpg style.
Lotus Turbo Challenge 2  //Behind view racing game. Best in the series.
Jaguar XJ220  //Another behind view racing game. Great music!
Cannon Fodder  //Funny mouse controlled shoot 'em up war game with tiny soldiers. "War's never been so much fun!".
Monkey Island 1 and 2  //This is what an adventure game should be like! (point&click)
Pinball Dreams, Pinball Fantasies, Pinball Illusions  //You probably know about these already. I Really love the music in all of them!
Benefactor  //Platformer/puzzle. Rescue and guide tiny men to the level exit. a bit like lemmings. but as a platformer. By Digital Illusions, creators of Pinball Dreams... Great music by Olof Gustafsson in this one also.
Slam Tilt  //This one is like Pinball Illusions 2. Fantastic looking game! 
Project X  //Side scrolling space shooter. Gradius-like power up system. Great looking!
Turrican 2  //My all time favorite 2D action/platformer. Really great music by Chris Hülsbeck!